1. Field of the Invention
The present invention relates to a Schottky diode utilizing diamond as a semiconductive material.
2. Related Background Art
Diamond is known as a unique semiconductor. It is suitable for use in electronic devices operating at high speed, high power or under harsh climatic conditions. For example, diamond exhibits electron and positive hole mobility of 2,000 and 2,100 respectively, which are sufficiently high in comparison with those of Si (1,500; 450), GaAs (8,500; 400) or 3C-SiC (1,000; 70). Also, the thermal conductivity and the energy band gap of diamond are significantly larger than those of other semiconductive materials. Tab. 1 shows the comparison of these properties, extracted from N. Fujimori, "Handbook of Synthetic Diamond" and Setaka et al;., Science Forum, Tokyo, 1989.
TABLE 1 ______________________________________ Si GaAs 3C-SiC Diamond ______________________________________ Energy gap[eV] 1.1 1.4 2.2 5.5 Thermal conductivity 1.5 0.5 4.9 20.0 [W/cmK] Electron mobility 1500 8500 1000 2000 Positive hole mobility 450 400 70 2100 [cm.sup.2 /V.sec] ______________________________________
However, these excellent properties can only be exhibited in a monocrystalline layer, and can hardly be reflected in electronic devices in case of an amorphous or polycrystalline structure involving many imperfections. Up to the present, diamond in monocrystalline structure could only be obtained as a natural product, by synthesis under high temperature and high pressure, or by homoepitaxial growth of thin monocrystalline layer on such natural or synthesized diamond. Consequently diamond is unfavorable in terms of productivity, economy and limitation in space as a substrate in comparison with other semiconductive materials.
On the other hand, deposition of diamond on Si or SiO.sub.2 does not provide a monocrystalline layer but a polycrystalline layer in which minute monocrystalline domains are mutually separated by domain boundaries as reported by B. V. Derjaguin et al., J. Crystal Growth 2 (1986) 380; S. Matsumoto et al., Jpn. J. Appl. Phys. 21 (1982) L183; and H. Kawarada et al., Jpn. J. Appl. Phys. 26 (1987) L1031.
A device formed on such polycrystalline layer cannot exhibit sufficient device characteristics due to a potential barrier against carrier movement, formed by the domain boundary.